1. Field of the Invention
The present invention relates to a thermally assisted magnetic recording head with an optical waveguide for thermal assistance. In particular, the present invention relates to a thermally assisted magnetic recording head with a pair of dummy optical waveguides for alignment in order to align with a light source with high precision, and a primary optical waveguide for thermal assistance.
2. Description of the Background Technology
In the field of magnetic recording using a head and a medium, further improvements have been demanded in performance of thin film magnetic heads and magnetic recording media in view of an increase in recording density of magnetic disk devices. For the thin film magnetic heads, composite type thin film magnetic heads formed by lamination of a reading magnetoresistive (MR) element and a writing electromagnetic conversion element are being widely used.
In contrast, the magnetic recording medium is a so-called non-continuous medium, in which magnetic particles are aggregated. Each magnetic particle has a single magnetic domain. Here, a single recording bit is formed by a plurality of magnetic particles. Therefore, to increase magnetic density, the size of the magnetic particles must be reduced, and asperity at a border of recording bits needs to be minimized. However, if the size of the magnetic particles is reduced, there is a problem that thermal stability for magnetization of the magnetic particles is lowered as the volume of the magnetic particles is reduced.
To address this problem, increasing magnetic anisotropic energy Ku of magnetic particles may be considered. However, this increase in Ku causes an increase in anisotropic magnetic field (coercive force) of the magnetic recording medium. On the other hand, the upper limit of the writing magnetic field intensity for the thin film magnetic head is determined substantially by a saturation magnetic flux density of a soft magnetic material forming a magnetic core in the head. As a result, when the anisotropic magnetic field of the magnetic recording medium exceeds an acceptable value determined from the upper value of the writing magnetic field intensity, writing becomes impossible. Currently, as a method to solve such a problem of thermal stability, a so-called thermally-assisted magnetic recording method has been proposed, which uses a magnetic material with a large Ku, which also performs the writing by heating the magnetic recording medium immediately before applying the writing magnetic field to reduce the anisotropic magnetic field.
For this thermally assisted magnetic recording method, a method that uses a near-field probe, a so-called plasmon antenna, is known. The near-field probe is a piece of metal that generates near-field light from a plasmon excited by irradiated laser light. For example, a plasmon-generator that includes a metal scatterer having a shape of a cone or the like formed on a substrate is disclosed in U.S. Pat. No. 6,768,556.
In addition, a configuration is disclosed in U.S. Patent Publication No. 2004/081031 A1, in which a plasmon-generator is formed at a position to contact the main pole of a perpendicular magnetic recording head so that an irradiated surface of the plasmon-generator is perpendicular to the magnetic recording medium. Moreover, U.S. Patent Publication No. 2003/066944 A1 discloses a technology, in which irradiation of stronger near-field light onto the magnetic recording medium is attempted by preferentially positioning the front end of a plasmon antenna close to the magnetic recording medium.
The inventors of the present application have considered the potentiality of the magnetic recording by irradiation of the near-field light to be a breaking point and have been developing more improved thermally-assisted magnetic recording heads.
For performing thermally assisted recording by the irradiation of the near-field light with a magnetic recording head, it is necessary to integrate a laser light generating device, which is a light emitting element that is a light source, in the magnetic recording head, to take in laser light emitted from the laser light generating device into an optical waveguide, and to guide the laser light to a plasmon antenna located near a position facing the magnetic recording medium.
A method of forming a light source unit with a light source on a light source supporting substrate separate from a slider which is then overlaid and fastened to a surface on a side opposite to an air bearing surface (ABS) of a slider can produce a thermally assisted magnetic head with favorable yield because the slider with the magnetic head part and the light source unit are independently tested and then a proper slider and light source unit are fastened together. Furthermore, in this case, the light source can be provided at a location away from the ABS and in proximity to the slider. Therefore, there are merits that the light propagation efficiency is favorable and the configuration of the entire device is simplified.
However, precise alignment of the light source and the waveguide when fastening the slider and the light source unit is not easy. Poor alignment precision leads to lower heating efficiency of the medium and major problems occur when performing thermally assisted magnetic recording.
In order to resolve these problems, means for enhancing alignment precision between the light source and the waveguide is disclosed in US Patent Publication 2008/0055784 (JP Unexamined Patent Application 2008-059694). Therein, means is proposed where a first waveguide and a second waveguide are provided at a prescribed interval, and a first alignment process is performed using the second waveguide so as to maximize light intensity. Next, after the first alignment process, a second alignment process is performed where the light source unit is moved in a predetermined direction and distance based on the positional relationship between the second waveguide and the first waveguide.
The aforementioned proposal is based on an extremely excellent concept; however, precisely aligning the light source and the waveguide so as to maximize the light intensity using one waveguide in the first alignment process is an operation that requires time, and determining the alignment precision is difficult.
The present invention further improves on the aforementioned proposed technology, and provides a head structure that allows simple and higher precision alignment between the light source and the waveguide when fastening the slider and the light source unit.